Purification of sugar solutions



Patented Jan. 30, 1951 PURIFICATION OF SUGAR SOLIPIIUNS Robert Roger Bottoms, Cre'stwood, and Ernest h.

Pittman, Elizabethtown, Ky., assignots to National Cylinder Gas Company, Chicago, 111., a

corporation of Delaware No Drawing. Application March 26, 1947,

' Serial No. 7 37,406

11 Claims.

1 This invention relates to the production of white sugar from sugar containing juices, syrups or solutions, and involves certain novel steps employed for purifying or defecating the solu-.

tion to remove colloids and color forming mate- Although our new process is adapted for treating various sugar containing solutions it is particularly eifective and important in the purification or defecation of cane sugar juices and syrups.

We have discovered that the removal of the colloids and color forming materials may be effected more economically, efiiciently and completely by the use of a hydrated calcium silicate, than is possible when using any of the commonly employed agents with which we are familiar.

By the use of hydrated calcium silicate we are able to secure a white sugar directly from cane syrups which sugar will remain white without any further refining. The sugar is much whiter than direct consumption sugar produced by other methods. and will not turn yellow in storage as other direct consumption sugars as heretofore produced usually do. The hydrated calcium silicute is an inexpensive material and therefore the sugar can be produced at a lower cost than when other processes are employed. Furthermore all of the available sugar in the solution can be obtained as white sugar, whereas in using other processes it is generally necessary to dispose of a considerable portion of the available sugar by selling it as high grade molasses. In the installation of our process in a sugar factory nornially making raw sugar the cost of additional equipment for operating in accordance with our new process is very low.

-. The hydrated calcium silicate which we employ is highly alkaline in reaction and has a pH of about 10. This'alkaline reaction is important in flocculating the colloids. *In the action of hydrated calcium silicate on the syrup the calcium component of the compound reacts with acidic components contained in the solution and a highly active flocculated silica is released. This silica coagulates the colloids and by adsorbent action removes the materials which cause color formation in the sugar.

In practice the process may be carried out as follows. The raw juice is clarified in the usual way which is practiced in mostsugar factories, or it may be specially treated, as for example by the addition of a small amount of finely divided siliceous material together with lime, and then heated. The colloidal material which separates in this step settles out as a "mu and the clear juice is run to the evaporators. This juice is then concentrated to a syrup which may have a density of from to Brix. The syrup thus produced is then treated by the process constituting the main novel feature of our invention.

To the hot syrup as above produced there is first added from about 0.1% to about 0.5% of its weight of finely divided, hydrated calcium silicate, and the temperature of the mixture is then raised to a point in the range of C. to C. while stirring. This treatment results in the precipitation of a large amount of colloidal nonsugars and color forming materials which remain in suspension in the heavy syrup. The pH of the syrup may then be adjusted to a value within the range of 6 to 7 by the addition of phosphoric acid. Activated decolorizing carbon or other decolorizing agent is then added in a quantity from about 0.1% to about 0.5% of the weight of the syrup, and the syrup is permitted to stand for about ten minutes after which it is filtered or otherwise treated to remove all suspended solid materials. The filtered pr clarified syrup is then passed to the crystallizing pans and further concentrated to crystallize the sugar. The massecuite thus produced is then centrifuged and washed in the conventional manner to produce a white direct consumption sugar.

The hydrated calcium silicate which we employ does not occur in nature, but may be prepared in various known ways, for example, as shown in Patent No. 2,287,700 to Muskat et all. Its content is approximately C20, 18% to 21%, andSiOz, 66% to 69%, the balance being water of hydration and a small amount of impurities.

The pH is approximately 10, and the particle size of the aggregates is approximately 10 microns.

The pH and the ultimate particle size may vary For most cases the silicate should have an average ultimate particle size less than one micron, preferably not substantially in excess of 0.5 micron. While a small quantity of agglomerates or particles greater in diameter than one micron may be present, it is preferred that a preponderance of the particles generally not less than about 96 percent of the pigment particles be under one micron in size.

' hard upon drying and agglomerate to an undeiirable degree.

The method of preparing the calcium silicate also is of importance. Imaccordance with the present invention, it is found essential to prepare the silicate by precipitation from an aqueous solution of a soluble calcium salt. Calcium chloride is found to be most suitable for this purpose although other salts such as calcium nitrate or acetate may be used. While the calcium silicate may be prepared from calcium hydroxide slurries, the product is not as suitable as that obtained from salt solutions and often fails to cure satisfactorily. The precipitation is conducted by interaction of the calcium salt with a suitable soluble silicate such as sodium or other alkali metal silicate. In order to avoid the formation of hard products which agglomerate upon drying it is found desirable to precipitate the silicate from a concentrated solution containing not substantially less than 50 grams and preferably at least 75 grams of calcium chloride per liter, using sodium silicate solutions of about 100 grams SiOz per liter of solution and thereby to form a slurry containing not substantially less than 25 grams and preferably not in excess of 125 grams of calcium silicate per liter of slurry. While some departure from these conditions is possible, it is found preferable to adjust concentrations of calcium chloride within the specified range to insure formation of a suitable pigment.

The temperature of precipitation should be maintained at room temperature or above for most cases. The precipitated silicate may be recovered by decantation and/ or filtration and dried at a temperature sufliciently high to remove any water. The dried product is found to be very white and to have an average particle size below one micron. In general, it contains a quantity of water probably in the form of water of crystallization generally not in excess of 25 percent. This water is tenaciously retained by the silicate.

The following example is illustrative:

A quantity of calcium silicate was prepared by agitating an aqueous solution containing 100 grams per liter of calcium chloride with aqueous solution of sodium silicate having the formula N2120('SiO2)3.3s at a temperature of 25 C. This sodium silicate solution contained 100 grams per liter SiO2. The mixture was vigorously agitated for minutes to prevent agglomeration, after which the calcium silicate was recovered by filtration and was washed, dried at a temperature of 105 C. and finally pulverized and screened to produce a product having an average particle size less than one micron. The ratio of SiOz to 03.0 in this silicate was approximately 3.36.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. The method of decolorizing sugar bearing solutions containing non-sugars, which includes the step of coagulating non-sugars in such sugar bearing solutions in syrup form by the action of a finely divided, highly alkaline, hydrated calcium silicate having a composition corresponding to approximately 18% to 21% C20, approximately 66% to 69% $10,. the balane being Sub stantlally all water of hydration.

2. The method of decolorizing sugar bearing solutions containing non-sugars, which includes the step of coagulating the non-sugars in such sugar bearing solutions in syrup form by the action of a finely divided hydrated calcium silicate and having a pH of about 10 and having a composition corresponding to approximately 18% to 21% 0:10, approximately 66% to 69%' SiOz, the balance being substantially all water of hydration. 7

3. The method of decolorizing sugar bearing solutions containing non-sugars, which includes the steps of treating such sugar bearing solutions in syrup form with from about 0.1% to about 0.5% of finely divided, highly alkaline hydrated calcium silicate having a composition corresponding to approximately 18% to 21% CaO, approximately 66% to 69% SiOz, the balance being substantially all water of hydration, and heating and filtering the treated syrup.

4. The method of decolorizing sugar bearing solutions containing non-sugars, which includes the steps of treating such sugar bearing solutions in syrup form with from about 0.1% to about 0.5% of finely divided, highly alkaline hydrated calcium silicate having a composition corresponding to approximately 18% to 21% CaO, approximately 66% to 69% SiOz, the balance being substantially all water of hydration, heating to a temperature of 75 C. to 0., and filtering the treated syrup.

5. The method of decolorizing sugar bearing solutions containing non-sugars, which includes the steps of treating such sugar bearing solutions in syrup form with from about 0.1% to about 0.5% of finely divided, highly alkaline hydrated calcium silicate having a composition corresponding to approximately 18% to 21% C210, approximately 66% to 69% SiOz, the balance being substantially all water of hydration, heating to t a temperature of 75 C. to 120 C. and thereafter removing residual color by the action of a decolorizing agent and filtering.

6. The method of producing white sugar from cane juice, which includes clarifying the juice, concentrating the juice to a syrup having a density of from 40 to 60 Brix, adding to the hot syrup from about 0.1% to about 0.5% of finely divided, highly alkaline hydrated calcium silicate having a ratio of SiOz to 05.0 of not less than about 3 to 1, heating to 75 C. to 120 C. to precipitate colloidal and color forming materials, removing residual color forming materials by the action of activated decolorizing carbon, and hitering.

7. The method of'decolorizing sugar bearing solutions containing non-sugars, which includes the steps of treating such sugar bearing solutions in syrup form with from 1% to 5% of finely divided, highly alkaline hydrated calcium silicate having a. composition corresponding to approximately 18% to 21% Geo, and approximately 66% to 69% SiOz, the balance being substantially all water of hydration, heating to a temperature of 75 C. to 120 C., and adding phosphoric acid to adjust the pH to a value within the range of 6 to 7.

8. The method of decolorizing sugar bearing solutions containing non-sugars, which includes the step of coagulating non-sugars and colorforming impurities in such sugar bearing solutions in syrup form by the action of a suitable small quantity of finely divided precipitated calcium silicate having an average ultimate particle size not substantially in excess of about one micron, the molecular ratio of 8102 to CaO in said silicate being not less than about 2 to 1.

9. The method of decolorizing sugar bearing solutions containing non-sugars which includes the step of coagulating non-sugars and colorforming impurities in such sugar bearing solutions in syrup form by heating the same in intimate contact with a suitable small quantity of finely divided precipitated calcium silicate having an average ultimate particle size not substantially in excess of about one micron, the molecular ratio of SiOz to CaO in said silicate being not less than about 2 to l, and thereafter separating said silicate from said syrup bearing solution.

10. The method of decolorizing sugar bearing solutions containing non-sugars which includes the step of coagulating non-sugars and colorforming impurities in such sugar bearing solutions in syrup form by heating the same in intimate contact with a suitable small quantity of finely divided precipitated calcium silicate having an average ultimate particle size not substantially in excess of about one micron, the molecular ratio of SiOz to CaO in said silicate being not less than about 3 to 1, and thereafter separating said silicate from said syrup bearing solution.

11. A method of producing white sugar from cane sugar bearing solutions containing nonsugars and color-forming impurities which includes the steps of heating such sugar bearing solutions in syrup form in intimate contact with a suitable small quantity of finely divided precipitated calcium silicate having an average ultimate particle size not substantially in excess of one micron, the molecular ratio of SiOz to CaO of said silicate being not less than 3 to 1, adjusting the pH of the treated syrup to a value within the range of about 6 to 7, and thereafter filtering the treated syrup.

ROBERT ROGER BO'I'IOMS.

ERNEST E. PITTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,579,090 Deguide Mar. 30, 1926 1,653,491 Borden Dec. 29, 1927 FOREIGN PATENTS Number Country Date 2,358 Great Britain Of 1853 62 Great Britain of 1869 1,576 Great Britain of 1914 OTHER REFERENCES Mellor, Comp. Treatise on Inorg. and Theoret. Chem., London 1925, vol. VI. PD- 358-365. 

6. THE METHOD OF PRODUCING WHITE SUGAR FROM CANE JUICE, WHICH INCLUDES CLARIFYING THE JUICE, CONCENTRATING THE JUICE TO A SYRUP HAVING A DENSITY OF FROM 40* TO 60* BRIX, ADDING TO THE HOT SYRUP FROM ABOUT 0.1% TO ABOUT 0.5% OF FINELY DIVIDED, HIGHLY ALKALINE HYDRATED CALCIUM SILICATE HAVING A RATIO OF SIO2 TO CAO OF NOT LESS THAN ABOUT 3 TO 1, HEATING TO 75* C. TO 120* C. TO PRECIPITATE COLLOIDAL AND COLOR FORMING MATERIALS, REMOVING RESIDUAL COLOR FORMING MATERIALS BY THE ACTION OF ACTIVATED DECOLORIZING CARBON, AND FILTERING. 